Saw blade guard

ABSTRACT

A saw blade guard is movable between an upper housing and a generally horizontal work support table disposed below and spaced from the housing. An unconfined portion of a blade is disposed between the housing and work table, the blade guard forming a barrier between the unconfined blade portion and an operator. The guard is in the form of a channel-shaped member disposed in confronting relation and spaced from the blade to present a barrier between the blade and the operator. The upper portion of the channel member is slidably mounted for vertical movement. The guard member is fully extended in full guard position when the member extends from the housing to a position adjacent the work table and may be manually raised to any desired degree of elevation along the otherwise exposed edge of the blade to thereby provide access to a selected portion thereof for operation on a work piece. A solenoid, mounted on the housing is connected to an engaging slide member which controllably engages a toothed rack mounted lengthwise on the guard member. The engaging slide member, controlled by the solenoid, engages the toothed rack to maintain the guard member at a selected vertical position above the work table when the saw is in operation and releases the guard member and permits the same to drop to the level of the work table under the action of gravity to substantially enclose the blade when the saw is not in operation.

United States Patent l 'l Weissman I 1 SAW BLADE GUARD Bernard Weissman.225 l. 48th St. New York NNY l lfll7 |22 Filed: Sept. I4 1973 121] ApplNo: 397450 [76] inventor:

I56| References Cited UNl lliD STATES PA lFNlS 1149.063 3/1930 Brown. .vv l 83/814 X 2,371 731 3/1945 lioice et al l l l l i i l v v 83/8 l42579,9 55 12/1951 ()rescan i i 83/100 3104688 9/l963 Bretthuucr v a i ii i 83/814 FOREIGN PATENTS ()R APPLICATIONS 78186 4/1919 Austria 83/814Primary Iituminer-Donald R. Schran Attorney. Agent or firm-Friedman &Goodman [57] ABSTRACT A saw blade guard is movable between an upperhous- 1 1 June 10,1975

ing and a generally horizontal work support table dis posed below andspaced from the housing. An uncon fined portion of a blade is disposedbetween the housing and work table the blade guard forming a barrierbetween the unconfined blade portion and an opera tori The guard is inthe form of a channel-shaped member disposed in confronting relation andspaced from the blade to present a barrier between the blade and theoperatorv The upper portion of the channel member is slidably mountedfor vertical movement. The guard member is fully extended in full guardposi tion when the member extends from the housing to a positionadjacent the work table and may be manually raised to any desired degreeof elevation along the otherwise exposed edge of the blade to therebyprovide access to a selected portion thereof for operation on a workpiece. A solenoid. mounted on the housing is connected to an engagingslide member which controllably engages a toothed rack mountedlengthwise on the guard member, The engaging slide member controlled bythe solenoid, engages the toothed rack to maintain the guard member at aselected vertical position above the work table when the saw is inoperation and releases the guard member and permits the same to drop tothe level of the work table under the action of gravity to substantiallyenclose the blade when the saw is not in operation,

14 Claims, 6 Drawing Figures PATENTEDJUM 10 I975 SHEET FIG! SHEETPATENTEI] JUN 10 I975 PATENTEDJuH 10 ms SHEET FIG. 5

FIG.6

SAW BLADE GUARD BACKGROUND OF THE INVENTION The present inventiongenerally relates to protective devices. and more particularly. to aguard member for power saws.

Various protective measures have been proposed for preventing injury inthe use of power tools. However. many of these proposed measures are notalways fullproofand depend for their effectiveness to a certain dc greeupon the steps taken by the operators of the machine. (overs and hoodsof various types are known which must be positioned manually to preventexpo sure of dangerous elements. such as saw blade teeth. For thisreason. the known protective devices are not always successful. Anoperator must take the necessary steps. for example when he hascompleted using a power tool. to prevent a hazardous condition tohimself or another user upon a subsequent use of the machine. However,inadvertancc of forgetfullness sometimes results in the preventivemeasures or steps not being taken and a hazardous condition may beestablished.

SUMMARY OF THE INVENTION Accordingly. it is an object of the presentinvention to provide a saw blade guard which is not possessed of theabove described disadvantages heretofore known in the prior artcomparable safety devices.

It is another object of the present invention to pro vide a saw bladeguard which operates automatically and does not depend on the stepstaken by the operator of the machine to prevent a hazardous condition.

It is still another object of the present invention to provide a sawblade guard which requires. as an additional safety measure. an operatorto utilize both hands to operate the machine from its guarded or safecondition.

It is yet another object of the present invention to provide a saw bladeguard which includes an override feature which permits a portion of theblade to be exposed in the protective mode of the guard.

It is a further object of the present invention to provide a saw bladeguard which is simple in construction and economical to manufacture.

It is still a further object of the present invention to provide a sawblade guard which is electrically and automatically operated and whichis adapted for integration with a safety circuit wherein the saw bladeguard is placed into operation whenever the power saw housing is opened.as for maintenance or repair purposes.

In order to achieve the above objects. as well as others which becomeapparent hereafter. a saw blade guard in accordance with the presentinvention will be described herein which is utilized in a power-operatedsaw having a vertically disposed saw blade wherein an upper portionofthe blade is enclosed in a housing and the blade extends through anaperture provided in a generally horixontal work support table disposedbelow and spaced from said housing and whereby an unconfined portion ofthe table is disposed between said housing and work table. The saw bladeguard of the present invention for forming a barrier between saidunconfined portion and an operator comprises an elongated barrier memberdisposed in confronting relation and spaced from the blade to present abarrier between the blade and the operator. The upper portion of thebarrier member is mounted in said housing for vertical movement and isfully extended in full guard position when said member extends from saidhousing to a posi tion adjacent said work table and may be manuallyraised to any desired degree of elevation along the otherwise disposededge of the blade to thereby provide access to a selected portionthereof for operation on the work piece. Locking means are provided forengaging said guard to maintain said enclosure at a selected verticalposition above the work table when the saw is in operation and torelease said guard and permit the same to drop to the level of the worktable under the action of gravity to substantially cover the blade whenthe saw is not in operation.

BRIEF DESCRIPTION OF THE DRAWINGS With the above and additional objectsand advantages in view. as will hereinafter appear. this inventioncomprises the devices, combinations and arrangements of partshereinafter described and illustrated in the accompanying drawings of apreferred embodiment in which:

FIG. I is a front elcvational view ofa band saw incorporating the sawblade guard in accordance with the present invention, showing portionsof the housing broken away to expose important features of the band saw;

FIG. 2 is a perspective view of the saw blade guard of the presentinvention shown in FIG. 1. showing a control solenoid and slide memberforming part of the locking device of the present invention with theupper saw wheel removed;

FIG. 3 is a fragmented rear clevational view of the lower portion of thesaw blade guard shown in FIGS. 1 and 2;

FIG. 4 is a cross-sectional view of the saw blade guard ofthe presentinvention taken along line 4-4 of FIG. 2, showing the two extremepositions of the guard for exposing and for covering the saw bladeportion which acts upon a work piece;

FIG. 5 is a fragmented cross sectional view of a guide and bearingprovided for the saw blade. taken along 55 in FIG. I; and

FIG. 6 is an electrical schematic for the circuit which controls theoperation of the band saw including the blade guard of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now specifically tothe drawings. wherein similar or identical parts have been designated bythe same reference numerals throughout. the present invention will bedescribed in connection with a band saw I0. It should be clear. from thedescription that follows. however, that the blade guard of the presentinvention can be utilized with any power tool wherein hazardouscomponents thereof must not be left exposed when the machine is not inuse. The present invention is particularly useful to protect operatorsof saws of various types. including band saws and jig saws.

The band saw includes a U-shaped enclosure I2 which includes upper andlower housings l4. l6 and a lateral connecting housing [8. The generaloutline of the enclosure is formed by U-shaped channels 20. Mounted onone side of the U-shaped channels is a back or rear wall 22. Hingedlyconnected to the other side of the U-shaped channels are upper and lowerhousing doors 24, 26 which can individually be opened to provide accessto the upper housing 14 or the lower housing 16 respectively.

A work support table 28. generally horizontally dis posed, is providedbelow and spaced from the upper housing 14. The work support table 28 isprovided with an aperture or slot 30 through which a circular saw bladeband 32 can extend. as to be more fully described hereafter.

Provided in the upper housing is a saw wheel 34 which is rotatablymounted on the rear wall 22. The saw wheel 34 can. for example. be madeof an elastomeric material such as nylon. Advantageously. a rubber stripof material 36 is provided about the peripheral or circumferentialsurface of the saw wheel 34 to provide better gripping action for thesaw blade 32. Conventional means (not shown) may be provided for raisingand lowering the upper saw wheel 34 within predetermined limits tofacilitate the mounting of the circular saw blade 32 and fixing thesame.

The work support table 28 is provided with an extension 38 disposed infront of the connecting housing 18. The extension 38 is removablymounted on the connecting housing 18 in any suitable or conventionalmanner whereby the platform or work table extension 38 may be removedfor mounting the circular blade band 32.

In the lower housing 16, there is provided a lower wheel 40 which is inthe nature of a belt pulley wheel. The pulley wheel 40 can similarly bemade of elastomeric material and is similarly provided with a strip ofrubber material 36 about its circumferential surface. The two saw wheels34, 40 are vertically aligned and spaced substantially equal distancesfrom the back or near wall 22 to permit mounting and carrying of thecircular saw blade 32 thereon.

The lower belt pulley wheel 40 is provided with a groove (not shown)suitable for receiving a pulley belt 42. Mounted in back of the rearwall 22 is a motor 44 for driving the band saw 10, the shaft 46 thereofextending through the rear wall 22 and being provided at the end thereofwith a belt pulley wheel 48 provided with spaced ridges (not shown)configurated to meshingly engage the ridges (not shown) on the interiorof the pulley belt 42. A slot (not shown) may be provided in the rearwall. through which one of the mounting screws to the motor passes topermit slight movements of the motor shaft 46 relative to a fixed axison which the bottom saw wheel 40 rotates for tightening the pul ley belt42.

Provided on one side of the bottom saw wheel 40 in the lower housing I6is a collecting chamber 50 disposed beneath the slot 30 in the worksupport table 28. The chamber or compartment 50 is formed by a straightwall portion 52 extending from the work table 28 to the periphery of thewheel 40. A curved wall portion 54 follows the contour of the peripheryof the bottom wheel 40. the curved wall portion 54 being provided withan opening 56 which communicates the interiors of the collecting chamber50 and the lower housing 16 along a circumferential portion of the lowersaw wheel 40. A further flat inclined wall portion 58 is provided, whichtogether with the other above de scribed wall portions 52, 54, definethe collecting chamber 50.

An opening 60 is provided at the lower end ofa channel member wall 61which is suitably connected to a vacuum system, such as a vacuumcleaner. for collecting the dust. shavings and the like which aretransmitted into the collecting chamber 50 by the saw blade 32.

Also provided in the collecting chamber 50. beneath the work supporttable 28, is a guide 62 which is provided with a slot 64 suitable toconfine the saw blade 32 and prevent excessive transverse movement ofthe blade in lateral directions, as shown in FIGS. 1. 4 and 5. Toprevent excessive transverse movement in a rearward direction, upon theapplication of a work piece the blade 32. a bearing 66 is mounted on thechannel member wall 61. the bearing 66 being rotatable to minimize thefrictional forces exerted on the saw blade 32 when the latter abutsagainst the hearing. The bearing 66 is movable to a limited degree infrontward and rearward directions by the provision of a slot (not shown)within the channel member wall 61 through which a supporting screw forthe bearing passes.

ln a band saw structure as above described, a circular saw blade 32 hasan operative portion 70 and a return portion 72. The operative portion70 extends from and is partially enclosed in the upper housing 14 whilethe lower end of the operative portion extends through the aperture orslot 30 provided in the generally horizontal work support table 28.Accordingly. there remains an unconfined portion 74 of the blade whichis disposed between the housing 14 and the work table 28. An importantfeature of the present invention is a saw blade guard 80. as to bedescribed. for forming a barrier between the unconfined portion 74 andan operator. In broad terms. the guard comprises an elongate barriermember 82 disposed in confronting relation and spaced from the blade 74to present a barrier between the blade and the operator. The operativeportion of the barrier member is mounted in the upper housing 14 forvertical movement and is fully extended in full guard position when themember 82 extends from the housing to a position adjacent the work table28. ln the presently preferred embodiment, the guard 80 may be manuallyraised to any desired degree of elevation along the otherwise exposededge of the blade 74 to thereby provide access to a selected portionthereof for operation on a work piece.

Examining the presently preferred embodiment of the blade guard in FIGSv24, this is shown to comprise a generally U-shaped channel or member 84which includes a slide or face plate 86 and front and rear side guardmembers 88. 90. The front side guard member 88 is advantageouslytransparent and made from a material such as Lucite or Plexiglas. Theslide or face plate 86 is provided with an elongate slot 92 which runssubstantially the entire length thereof. Mounted on the U- shapcdchannel 84 and forming part of the upper housing are two stops orbushings 94. 96 which are received within the slot 92. The upper stop 94is positioned on the U-shaped channel to abut against the upper end ofthe slot when the lower portions of the guard 80 are just above the worksupport table 28 and substantially enclose and cover the otherwiseunconfined blade portion 74. The lower stop 96 is mounted on theU-shaped channel 84 to engage the lower end of the slot to limit upwardmovement of the guard 80 when the unconfined portion 74 has beensubstantially exposed.

Provided at the lower end of the rear side guard member there isprovided a support bracket 98 on which a bearing support member [00 ismounted. The bearing support member [00 is provided with horizontalslots 102 which permit slidable movement of the hearing support member Irelative to the support bracket 98 for permitting limited lrontward andrearward movement of a bearing I04 (I-'l(i. 4) mounted on the bearingsupport member. A blade guide I06 is provided at the lower extremitiesof the bearing support in. rnber I00 having a slot I08 for limitingtransverse 11M =\ements of the blade. The bearing I04 and the biadeguide I06 are similar to the hearing 66 and guide 62 described inconnection with the collecting department or chamber 50 and serve thesame functions as the latter.

From the above description. it should be clear that the guard member 80,in its lower position wherein the stop 94 engages the upper end of theslot. substantially encloses the unconfined portion of the blade 74 andcffectively forms a barrier between the unconfined portion and anoperator. When using the machine, the guard member 80 can be raised byslidable movement thereof along the slot 92 to expose as much or aslittle of the unconfined blade portion 74 as desired.

It should be noted that the face plate 86, when slidably mounted asabove described. forms a continuation of the U-shaped channel or sidewall I of the upper housing I4. This results in an additional safetyfeature whereby an operator cannot inadvertently position a finger. forexample, into a space which may otherwise result. Also. thiscontinuation provides a finished effect which is aesthetically pleasing.

An important feature of the present invention is the provision oflocking means for the blade guard 80. Broadly. the locking means isprovided for engaging the guard 80 to maintain the same at a selectedvertical position above the work table 28 when the saw is in operationand for releasing the guard and permitting the same to drop to the levelof the work table under the action of gravity to substantially cover theblade 74 when the saw is not in operation.

A presently preferred locking means is shown in FIGS. I. 2, 4 and 6wherein an elongate toothed rack 112 is mounted lengthwise of the sloton the face plate 86 in back of the rear side guard member 90. Thetoothed rack I12 is provided with teeth 114 each having an upperinclined surface and a lower substantially horizontal surface to form aratchet tooth rack. Advantageously. the toothed rack I12 extendssubstantially along the entire length of the guard member 80.

Mounted on the rear wall 22 is an electromechanical device in the formof a solenoid 116. The solenoid I I6 is provided with a plunger II7which. in the embodi ment being described. moves towards the right, asviewed in FIGS. 1, 2 and 4. when energized. The sole noid 116 is mountedon a bracket 118. provided with a recess 120 through which an elongateengaging slide member I22 passes. One end of the engaging member isconnected to the plunger and the other end of the engaging memberextends through a retaining bracket I24 mounted on the rear wall 22whereby the engaging member 122 is slidably mounted in a direction alongits length in response to movements of the plunger II7.

The free end of the slide I22 which extends through the retainingbracket I24 is provided with a bent portion I26 and a tip I28 formed bycutting the end ofthe engaging member I22 at a slant to provide a lowerin clined edge I30. The pointed tip I28 of the engage ment member I22 isspaced from the rear wall 22 to assure engagement thereof with the teethll-I of the rack II2.

The angle at which the end of the engaging member is cut advantageouslycorresponds to the angle of the inclined surfaces of the teeth I14 onthe ratchet-type rack 112. The horizontal edge of the slide or engagingmember is adapted to engage a respective one of the horizontal teethsurfaces ofthe rack when the engaging member is fully advanced towardsthe latter Thus. the point I28 ofthe engaging member is complementary inconfiguration to the space formed between a horizontal surface of onetooth and an adjacent inclined surface of another tooth The stroke ofthe solenoid 116 is selected to cause the pointed end I28 oftheengagement member I22 to engage the rack I12 when energized whiledisengaging the slide engagement member from the rack when deenergized.

As should now be clear, when the solenoid I I6 is deenergized the guardcan be slidably moved between its upper and lowermost limits. For thispurpose a fin ger grip I30 is advantageously provided which facili tatesthe movement of the guard 80.

Referring now to the electrical schematic diagram of the circuit whichcontrols the operation of the band saw 10, the leads or wires 132 areconnectable to the power lines in a conventional manner. Each of theleads is connected to one pole of a double pole switch I34. One of theleads is further connected to a single pole. normally opened switch 136which serves as a tripping switch for the upper door 24 of the housing14, as will be more fully described hereafter. The motor 44 is connectedto the power lines via the aforementioned switches 134, I36.

Connected in parallel to the motor 44 is the primary winding of atransformer 140, the secondary winding of which is connected to thesolenoid 116 coil 142. A diode 144 is connected between the secondarywinding and one end of the solenoid coil while a series resistance 146is connected between the other end of the solenoid coil I42 and thesecondary winding. A capacitancc 148 is connected across the seriesconnection of the solenoid coil I42 and the resistance 146.

The diode 144 and the capacitance 148 to form a rectification circuitfor rectifying the alternating current presented at the secondarywinding to convert the same to a dc. current at the solenoid coil I42.The purpose for the series resistance 146 will be described hereafter.

The normally open switch 136 is closed when the upper housing door 24 isclosed. In this condition, when the main power switch 134 is closed. themotor 44 is energized and the band saw is placed into operation.Simultaneously. the solenoid I16 is energized and the slide engagingmember 122 is urged towards the right into engagement with the rack II2.

The operation of the guard member 80 will now be described. With theupper housing door 24 closed. and with the main power switch 134 in theoff position. the solenoid I16 remains deenergized and the sliding engaging member 122 is maintained disengaged from the rack 112.Accordingly. an operator may manually slidably move the guard 80 to anydesired elevation above the work table 28. As soon as the main poweron/off switch 134 is closed and the motor 44 is energized, the solenoidII6 is similarly energized and the sliding engaging member I22 is urgedtowards the right into engagement with the rack II2. Release of theguard member 80 by the operator does not result in the latter droppingto its lowermost position because of the rack engagement. Therefore,once an operator has selected a desirable elevation for the guide member80. the desired position thereofis maintained throughout the cuttingoperation by the locking means or the slide engagement member 122. Whenthe upper housing door 24 is opened or when the main power on/off switchI34 is closed, the solenoid 116 becomes deenergized and the slidingengagement member I22 is urged towards the left due to the spring loadedaction on the plunger 117. The resulting disengagement between thepointed end I28 of the slide member I22 and the rack 112 causes theblade guard 80 to drop to the level of the work table 28 under theaction of gravity to substantially cover the blade 74 when the saw isnot in operation. This forms an important feature of the present invention as it is not dependent on any conduct on behalf of the operatorof the machine but rather takes place automatically without any efforton his part. In this manner, both the operator as weli as others are notexposed to a dangerous or hazardous condition on a subsequent use of themachine.

The holding strength or power of the solenoid llb when energized, or theforce with which the slide en gaging member 122 is urged against therack 112, is a function of the current which llows through the sole noidcoil 142. By placing a series current limiting resistor I46 with thecoil 142, the holding strength can be adjusted. In the presentlypreferred embodiment, the holding strength of the solenoid 116 isadjusted to permit raising of the guard member 80 against the action ofthe pointed end I28 of the engagement member 122 wherein the lattersuccessively slidably abuts against the inclined surfaces of the rackteeth 114. However, it should be noted, that only raising of the guardmember 80 is possible, lowering the same not being permitted due to theengagement of the horizontal upper edge of the pointed end 128 and thehorizontal surfaces of the rack teeth 114. Thus, while raising of theguard member 80 is possible, this is more difficult than when themachine is turned off because of the engagement of the slide member withthe rack. In the selection of the resistor 146, care must be taken toselect a low enough resistance value which will assure sufficientcurrent through the solenoid coil 142 to assure the above de scribedengagement of the slide member 122 with the rack 112 when the solenoidis energized.

Numerous alterations of the structure herein disclosed will suggestthemselves to those skilled in the art. However, it is to be understoodthat the present disclosure relates to a preferred embodiment of theinvention which is for purposes of illustration only and is not to beconstrued as a limitation of the invention.

I claim:

1. in a power-operated saw having a vertically dis posed saw bladewherein an upper portion of the blade is enclosed in a housing and theblade extends through an aperture provided in a generally horizontalwork support table disposed below and spaced from said housing wherebyan unconfined portion of the blade is disposed between said housing andwork table, a saw blade guard for forming a barrier between saidunconfined portion and an operator, said guard comprising an eiongatedbarrier member disposed in confronting relation and spaced from theblade to present a barrier between the biade and the operator. the upperportion of said barrier member being mounted on said housing forvertical movement and is fully extended in full guard position when saidmember extends from said housing to a position adjacent said work tableand may be manually raised to any desired degree of elevation along theotherwise exposed edge of the blade to thereby provide access to aselected portion thereoffor operation on a work piece; and locking meansfor engaging said guard to maintain said enclosure at any one of aplurality of discreet selected vertical positions above the work tableupon actuation of the saw and to release said guard and permit the sameto drop to the level of the work table under the action of gravity tosubstantially cover the blade when the operation of the saw isterminated.

2. A guard as defined in claim I, wherein said barrier member is in theform of an elongate U-shaped channel.

3. A guard as defined in claim 2, wherein said U- shaped channel has aside facing the front of the saw made of a transparent material. wherebythe unconfined blade portion is visible when enclosing the latter in aguarding condition.

4. A guard as defined in claim 2, wherein a slot is formed in a side ofsaid barrier member, and stop means fixed on said housing and extendingthrough said slot, wherein vertical movement of said guard is limited byengagement of one of stop means and an end of said slot,

5. A guard as defined in claim I, further comprising blade guide meansprovided at the lower extremity of said guard for containing the bladeand preventing excessive transverse movements thereof,

6. A guard as defined in claim 5, further comprising adjusting means forpermitting limited movement of said guide means in a transversedirection.

7. A guard as defined in claim 1, wherein said housing has an end wall.and wherein said guard has a face slide surface substantially flush withsaid end wall in all vertical positions of said guard.

8. A guard as defined in claim 1, wherein said locking means comprises atoothed rack mounted lengthwise on said guard; slidahle engagement meansmounted on said housing for engaging said rack in a predeterminedposition thereof; and circuit means for moving said engagement means tosaid predetermined position only when the saw is in operation.

9. A guard as defined in claim 8. wherein said circuit means comprises asolenoid having a plunger fixed to said engagement means; and switchmeans for energizing said solenoid, said switch means alsosimultaneously energizing a motor which operates the saw.

10. A guard as defined in claim 9. wherein said solenoid is operated bydc. and wherein said circuit means is connected to a source of ac.power. and further comprising rectifier means for converting said a.c.power to dc. power.

ll. A guard as defined in claim 9, further comprising a resistanceconnected in series to the winding of said solenoid, wherein the holdingstrength thereof when energized can be adjusted to permit manualmovement of said plunger to move said guard against the action of saidengagement means,

12. A guard as defined in claim I]. wherein said rack is in the form ofa ratchet and has teeth with upper inclined surfaces, said engagementmember having a lower inclined edge substantially parallel to said upperinclined surfaces, whereby said guard may be forced in 10 ing chamberduring operation of the saw.

14. A guard as defined in claim 13. further comprising an opening in awall of said collecting chamber suitable to permit coupling thereto of avacuum hose for drawing away of said shavings and dust and preventingaccumulation thereof within said collecting chamber.

1. In a power-operated saw having a vertically disposed saw bladewherein an upper portion of the blade is enclosed in a housing and theblade extends through an aperture provided in a generally horizontalwork support table disposed below and spaced from said housing wherebyan unconfined portion of the blade is disposed between said housing andwork table, a saw blade guard for forming a barrier between saidunconfined portion and an operator, said guard comprising an elongatedbarrier member disposed in confronting relation and spaced from theblade to present a barrier between the blade and the operator, the upperportion of said barrier member being mounted on said housing forvertical movement and is fully extended in full guard position when saidmember extends from said housing to a position adjacent said work tableand may be manually raised to any desired degree of elevation along theotherwise exposed edge of the blade to thereby provide access to aselected portion thereof for operation on a work piece; and lockingmeans for engaging said guard to maintain said enclosure at any one of aplurality of discreet selected vertical positions above the work tableupon actuation of the saw and to release said guard and permit the sameto drop to the level of the work table under the action of gravity tosubstantially cover the blade when the operation of the saw isterminated.
 2. A guard as defined in claim 1, wherein said barriermember is in the form of an elongate U-shaped channel.
 3. A guard asdefined in claim 2, wherein said U-shaped channel has a side facing thefront of the saw made of a transparent material, whereby the unconfinedblade portion is visible when enclosing the latter in a guardingcondition.
 4. A guard as defined in claim 2, wherein a slot is formed ina side of said barrier member, and stop means fixed on said housing andextending through said slot, wherein vertical movement of said guard islimited by engagement of one of stop means and an end of said slot.
 5. Aguard as defined in claim 1, further comprising blade guide meansprovided at the lower extremity of said guard for containing the bladeand preventing excessive transverse movements thereof.
 6. A guard asdefined in claim 5, further comprising adjusting means for permittinglimited movement of said guide means in a transverse direction.
 7. Aguard as defined in claim 1, wherein said housing has an end wall, andwherein said guard has a face slide surface substantially flush withsaid end wall in all vertical positions of said guard.
 8. A guard asdefined in claim 1, wherein said locking means comprises a toothed rackmounted lengthwise on said guard; slidable engagement means mounted onsaid housing for engaging said rack in a predetermined position thereof;and circuit means for moving said engagement means to said predeterminedposition only when the saw is in operation.
 9. A guard as defined inclaim 8, wherein said circuit means comprises a solenoid having aplunger fixed to said engagement means; and switch means foR energizingsaid solenoid, said switch means also simultaneously energizing a motorwhich operates the saw.
 10. A guard as defined in claim 9, wherein saidsolenoid is operated by d.c. and wherein said circuit means is connectedto a source of a.c. power, and further comprising rectifier means forconverting said a.c. power to d.c. power.
 11. A guard as defined inclaim 9, further comprising a resistance connected in series to thewinding of said solenoid, wherein the holding strength thereof whenenergized can be adjusted to permit manual movement of said plunger tomove said guard against the action of said engagement means.
 12. A guardas defined in claim 11, wherein said rack is in the form of a ratchetand has teeth with upper inclined surfaces, said engagement memberhaving a lower inclined edge substantially parallel to said upperinclined surfaces, whereby said guard may be forced in an upwarddirection with said inclined edge slidably abutting said inclinedsurfaces.
 13. A guard as defined in claim 1, wherein the saw is providedwith a lower housing, further comprising a substantially closedcollecting chamber below said aperture in said work support table, saidblade passing into said chamber subsequent to cutting operations,whereby shavings and dust are drawn in to said collecting chamber duringoperation of the saw.
 14. A guard as defined in claim 13, furthercomprising an opening in a wall of said collecting chamber suitable topermit coupling thereto of a vacuum hose for drawing away of saidshavings and dust and preventing accumulation thereof within saidcollecting chamber.